Dr. Bamshad is trying to find genes that influence the positioning of organs inside the chest and abdomen (e.g., place the spleen and the liver on the left side and right side of the abdomen respectively). These abnormalities are called laterality defects. Individuals with laterality defects sometimes have structural defects of the heart (e.g., a hole between the chambers of the heart) or neural tube defects (e.g., spina bifida). Laterality defects including abnormalities of the heart and neural tube are commonly found in more than 1 individual within a family. Furthermore, these defects are clearly transmitted, at times, between parents and their offspring. Dr. Bamshad is studying these families to determine what genes are responsible for these defects. To do so, he must comprehensively evaluate each family to determine who is affected. This evaluation includes a physical examination, an abdominal ultrasound, a chest radiograph, and an echocardiogram. To date, three large families with laterality defects have been evaluated . In one of these families, preliminary evidence that a gene causing heart defects and misplaced organs is located on chromosome 3 was found.